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1.
Someone whose ass emits an odor strong enough to create casualties reminiscent of WWI's Mustard Gas.
Mike 'Mustard Ass' Dukes, has a weapon of extraordinary proportions in his arsenal.
by Krazy Kraka February 24, 2004
 
2.
A yellowish tint on your toilet paper without going #2 caused by sweaty ass and not using toilet paper corectly
Man Ive worked all day in this heat I bet I got mustardass.
by superskaggs August 29, 2009